Modelling for diagnosis in Modelica - implementation and analysis
Technical systems of today are often complex and integrated. To
maintain operational functionality and security it is sometimes
necessary to have a surveillance system which can detect a fault in an
early stage. The device that detects and locates the faulty component
is called a diagnosis system. There are several different approaches
to fault diagnosis, this study focus on a part of technical diagnosis
that uses a model of the system for assistance to make the
diagnosis. In the creation of the model of the system computer tools
can be used, in this thesis it is investigated if one such software
tool is practical to use in the building of the model of the system.
One aspect of technical diagnosis based on models is the creation of a
model of the process in question with support for faults, a fault
model. In this thesis, Modelica is used to create fault models. The
models produced from Modelica are then analyzed by some existing
diagnosis algorithms. The approach of designing fault models in
Modelica and then exporting the corresponding system and perform
diagnosis analysis on it in Matlab is considered feasible. But the
process falls a bit short of the aim of a automatic model building and
and diagnosis analysis procedure.
If the results from this thesis are to be used in the future will
depend on if the freedom that Modelica gives in designing fault models
are deemed worthwhile to accommodate so that the results from the
modeling suits the diagnosis analysis. One way to do ease this
transformation of data is to restrict the freedom of model designs in
Modelica but then some of the benefit that Modelica brings is negated.
It is shown here however that it it possible to design fault models in
Modelica and then use the results to analyze the models regarding
sensor placement and test design.
Olof Bäck
2008
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